Tiejun Zhao

We investigated the effects of a root-restricted cultivation experiment of netted melons in a greenhouse in south China over two cropping seasons (autumn–winter and spring–summer) with three root-zone volumes (R1: 15 L/plant, R2: 5 L/plant, and R3: 0.75 L/plant) on fruit production and quality. Seasonal temperature and light conditions significantly regulate the balance between yield and quality of netted melons. The high-temperature and strong-light environment in summer promotes vigorous plant growth, fruit expansion and the formation of coarse reticulation, achieving high yield, but it leads to a significant reduction in the content of soluble solids, Vc, soluble protein and antioxidant substances. Under the low-temperature and weak-light conditions in autumn, plants increase the angle between stems and leaves to enhance light interception. Although the fruits are small and the reticulation is fine, they accumulate higher levels of sugar, nutrients and antioxidant substances due to the large diurnal temperature difference. Furthermore, the effect of root restriction cultivation is significantly climate-dependent: severe root restriction (R3) can increase the harvest index in both seasons and improve the fineness of the reticulation in autumn, but it inhibits growth. Therefore, root-zone volume is the key to regulating comprehensive performance, and strategies should be optimized in combination with the climate background: moderate (R2) root restriction in autumn is suitable for improving quality and yield, while severe root restriction (R3) in summer has potential applications in specific quality indicators.

To ensure the year-round efficient production of high-quality cherry tomatoes, this study evaluated how four cherry tomato cultivars can enhance yield and quality through optimized nutrient solution and supplementary lighting. Nutrient solutions (N1 and N2) were adjusted, with EC at 1.6 dS/m (N1: nitrogen 10.7 me/L, phosphorus 2.7 me/L, potassium 5.3 me/L) during flowering stage, and 2.4 dS/m (N1: nitrogen 16 me/L, phosphorus 4 me/L, potassium 8 me/L; N2: nitrogen 10.7 me/L, phosphorus 5.4 me/L, potassium 10.8 me/L) from fruit setting to harvest. N1 used standard adjustments, while N2 was optimized by adding solely with KCl and KH₂PO₄. Lighting treatments included L1 (natural light) and L2 (supplemental red/blue light). The application of N2 effectively decreased nitrate levels while it significantly enhanced the content of soluble sugars, flavor, and overall palatability, especially fruit coloring in cherry tomatoes, irrespective of supplementary lighting conditions. However, such optimization also increased sourness or altered the sugar–acid ratio. Supplementary lighting generally promoted the accumulation of soluble sugars, sweetness, and tomato flavor, although its effects varied markedly among different fruit clusters. The combination of optimized nutrient solutions and supplementary lighting exhibited synergistic effects, improving the content of soluble sugars, vitamin C, proteins, and flavor. N1 combined with L2 achieved the highest plant yield. Among the cultivars, ‘Linglong’ showed the greatest overall quality improvement, followed by ‘Baiyu’, ‘Miying’, and ‘Moka’. In conclusion, supplementary lighting can enhance the effect of nitrogen on yield and amplify the influence of phosphorus and potassium on fruit quality improvement in cherry tomatoes. The findings of this study may serve as a theoretical basis for the development of year-round production techniques for high-quality cherry tomatoes.

Heat stress poses significant health risks to greenhouse workers, particularly during the summer season, including fatigue, dehydration, and severe heat-related illnesses. This makes continuous physiological monitoring an important task. Photoplethysmography (PPG), an optical technique that captures volumetric changes in peripheral blood circulation, offers an effective, non-invasive method for real-time cardiovascular system performance monitoring. Given the nonlinear and chaotic characteristics of PPG signals, traditional linear analysis methods cannot fully capture their complexity. This study applied recurrence quantification analysis, one of the methods of nonlinear time series analysis, to green and red light PPG signals collected under controlled and high-temperature greenhouse conditions. Analysis revealed significant changes in several recurrence quantification analysis indices, particularly those related to vertical structures within recurrence plots, indicating altered speed and duration of physiological state transitions under heat stress. These findings highlight the sensitivity of specific recurrence quantification analysis measures to heat-induced cardiovascular adjustments, reinforcing their utility for occupational health monitoring.

Photoplethysmography is a widely used technique to noninvasively assess heart rate, blood pressure, and oxygen saturation. This technique has considerable potential for further applications—for example, in the field of physiological and mental health monitoring. However, advanced applications of photoplethysmography have been hampered by the lack of accurate and reliable methods to analyze the characteristics of the complex nonlinear dynamics of photoplethysmograms. Methods of nonlinear time series analysis may be used to estimate the dynamical characteristics of the photoplethysmogram, but they are highly influenced by the length of the time series, which is often limited in practical photoplethysmography applications. The aim of this study was to evaluate the error in the estimation of the dynamical characteristics of the photoplethysmogram associated with the limited length of the time series. The dynamical properties were evaluated using recurrence quantification analysis, and the estimation error was computed as a function of the length of the time series. Results demonstrated that properties such as determinism and entropy can be estimated with an error lower than 1% even for short photoplethysmogram recordings. Additionally, the lower limit for the time series length to estimate the average prediction time was computed.

Photoplethysmogram (PPG) is one of the noninvasive biological signals widely used for the estimation of physiological parameters, such as heart rates in human health monitoring. Methods of its processing, its applications, and dynamics have been extensively investigated over the last several decades. However, there is still lack of the knowledge related to the fundamental structure of the PPG dynamics such as saddle equilibrium points, which have crucial importance to achieve the full understanding of the PPG dynamics and might provide useful information for establishing a mathematical model of the PPG. In this study, Morse graph theory was applied to the experimental PPG data in an attempt to verify the existence of saddle equilibrium and estimate its location with respect to the time-delay-reconstructed PPG attractor. The results demonstrated evidence that a saddle equilibrium point can be found in a neighborhood of the reconstructed PPG trajectory; moreover, it was found to be in the same reconstructed attractor’s region for healthy subjects from different age groups that points toward fundamental importance of the found saddle equilibrium for a general understanding of the PPG dynamics.